GBCartRead-PIC16

A PIC16-based Game Boy ROM dumper. Code is loosely based on InsideGadgets' Arduino implementation for technical details, see that site.

Includes schematic for the hardware and source (HI-TECH PIC C) for the firmware.

Required Hardware

• Gameboy cartridge header (or solder a pin header to your cartridge)
• PIC16F690 (any PIC with enough IOs - 15, including 8 bidirectional - and hardware UART should work)
• 2x 74xx594 shift registers (595s will work with changes to code)
• MAX232 or equivalent level shifter
• Handful of passive components (4x 1uF capacitors, 4x 10Kohm reistors)
• 5V regulated power supply
• a serial port

Building

Ideally it should be built in MPLAB (or MPLAB X), but the supplied makefile should work standalone.

1. Load project in MPLAB X
2. Configure compiler path if necessary
3. Run Build Clean

Using

1. Flash the hex to the PIC
2. Connect the cartridge and serial cable
3. Run some terminal program on the COM port: 9600 baud, 8 bits, no parity, 1 stop bit
4. Switch everything on
5. Use menu

Menu Options

• O: dump rOm
• A: dump rAm
• Z: run diagnoZtics
• i: interactive mode

Diagnostics

Performs a few actions that you can test, ideal for making sure your hardware works. Runs through several writes/reads to different parts, showing the expected result. Hit any key at each prompt to advance to the next test. Critically, WR should be tested before attempting a RAM dump. Pokemon have been lost due to a faulty WR pin.

Interactive Mode

• S: set address lines to the following value (reads 4 hex digits, uppercase only).
• R: read cartridge at current address.
• H: hexdump the first 512 bytes of the cartridge.
• X: go back to the main menu.

Code

• base.h deals with PIC-specific stuff.
• shiftreg.h & shiftreg.c handle driving a '594 shift register (two in this case)
• usart.h & usart.c handle comms.
• main.c does everything else.

The #ifdef __amd64 is used to inject alternate implementations or define PIC-specific variables for AMD64 targets. This allows tests to be run on a PC rather than having to flash and run on a real PIC.

Issues

• Avoid using loggers that log terminal content rather than raw input. PuTTY's logger will interpret backspace characters rather than writing them, which results in missing data. RealTerm works fine for this. Future work is to modify InsideGadgets' Python script to interoperate with this port.
• Apology to EEs: Decoupling capacitors are omitted from the schematic. These should be included for reliability.
• MAX3232s are more expensive than MAX232s. A MAX232 or 202 should work fine in place of the 3232.
• Writing RAM isn't supported yet.
• It's slow. The delay between address writes and data read/writes can be reduced to increase speed, but ultimately the limit will be set by the serial port. The UART can be driven faster - change the values in init() using the table on page 164 of the 16F690 Datasheet. I experienced strange behaviour past 9600 baud, and lacking an oscilloscope I decided to be patient rather than experiment blindly with decoupling capacitors.

Credit & Licence

The reading and writing algorithms are taken from InsideGadgets' implementation, licensed under the Creative Commons Attribution-NonCommercial 3.0 Unported License. Copyright: (c) 2011 insideGadgets - http://www.insidegadgets.com

The remainder of the implementation, including all other functionality (unless otherwise indicated) is copyright (c) 2012 Mathew Hall.

This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License.

http://creativecommons.org/licenses/by-nc/3.0/